The objective of this research is an understanding of the control mechanisms in avian oncovirus infection. Towards this end, two non-conditional mutants of Rous sarcoma virus have been isolated which are defective in viral replication. One mutant has a deletion in the polymerase gene which leads to synthesis of a non-functional protein. The second mutant is deficient in synthesis or processing of virion genomic RNA. Both of these mutants are being studied in order to understand in finer detail these events in the viral life cycle. We are also isolating and characterizing other mutant and recombinant viruses which exhibit changes in synthesis of viral coded proteins. Such aberrant viruses are also being utilized to elucidate the mechanism of recombination between avian oncoviruses. We are also studying the regulation of the endogenous avian oncovirus RAV-O by comparing recombinants between RAV-O and exogenous RSV which behave upon infection like RAV-O (restricted in some chicken cells) or RSV (not restricted). We hope to elucidate the biological parameters of control of RAV-O infection, as well as the biochemical site of cellular control.